1. Field of the Invention
This invention relates to a method of manufacturing a solderable laminar contact material having a layer of silver or non-oxidizable silver alloy and a cladding of silver in which an oxide of cadmium, and/or another oxidizable metal is substantially uniformly dispersed.
2. Description of the Prior Art
It is known from German Pat. No. 2,054,861 to produce a laminar contact material having a top layer of silver and cadmium oxide by cladding a base of silver or non-oxidizable silver alloy with a superimposed layer of silver-cadmium alloy by hot rolling, and by thereafter converting the cadmium in the top layer of cadmium oxide in an oxygen bearing atmosphere at elevated temperature. It is a disadvantage of the known process that the silver-cadmium alloy tends to oxidize while being heated to rolling temperature so that the interface is enriched with cadmium oxide, and that the bond between the two layers is weakened thereby.
It has been attempted to overcome this difficulty by bonding the two layers to each other at lower temperature and higher pressure, but is has been found that the bonding zone so produced contains voids into which cadmium migrates during the subsequent oxidation procedure. The interface between the two layers is enriched with cadmium oxide and the results are not significantly better than by conventional hot rolling.
It has further been proposed to superimpose a cold plate of silver-cadmium alloy on a plate of silver pre-heated to 200.degree. to 950.degree. C., to compress the two layers at 500 to 5000 kg/cm.sup.2, and to expose the resulting compound product to oxidizing conditions. A strong bond is achieved in this manner, but the process is inherently limited to batch operation and relatively costly.